The use of hydraulic pumps, such as power steering pumps, is well known in the automotive industry. Conventional hydraulic pumps, such as those used in power steering systems, are typically positive displacement pumps. Positive displacement pumps, such as gear pumps, have a pumping action that creates a pressure fluctuation in the pump discharge flow. Any variations in this pump discharge flow are converted to pressure pulsation when they encounter circuit resistance. This conversion is referred to in the art as a pressure ripple.
The pressure pulsations transmitted through the fluid can cause resonating of the system components downstream of the pump, which is known in the art as fluid borne noise. This pressure fluctuation or pulsation can also excite structures in the pumping circuit causing them to vibrate and generate additional objectionable noise.
Positive displacement pumps are typically driven by motors having motor shafts or drive shafts. Motor shafts are known to have fluctuations that are transmitted to the hydraulic or gear pump by direct coupling of the shaft to the hydraulic pump. These fluctuations further amplify the pressure pulsations transmitted through the fluid, thus increasing the objectionable fluid borne noise.
Other known couplings have been utilized between motor shafts and gear pumps, but most suffer from a variety of problems, including misalignment when driving one shaft to another. Additionally, these prior coupling devices are relatively expensive. It would therefore be desirable to provide an apparatus for coupling a motor shaft to a drive gear of a hydraulic pump for use in a power steering system that is able to minimize the amount of fluid borne noise attributable to the direct coupling and that is also inexpensive.